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Smiths Speedo Drive Confusion

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The speedo drive on my 850 is an original Smiths unit with the type number RS5330/168 and the ratio of 15:12.  I understand from the manuals that the correct type should be 5330/171.  Can anyone please tell me what the difference is? 

The unit appears correct for the diameter of the axle all be it that there is no way that the axle opening is large enough to take the Speed Drive Spacer (06.7629) that the parts list suggests.

 

Regards to all.

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I am not familiar with Commando's but know enough to say  its an area where its easy to get it wrong and it can be costly and dangerous.  Some illustrations show the small drive unit  axle spacer as a loose item , but on earlier Nortons  its normally  fixed  in the drive box. If you get the assembly wrong  its possible to crush the drive ( which does need to be clamped in tightly ) . A crushed drive will usually buckle and rub/bind on the alloy hub cover and as the drive is cast alloy it will be weakened or fracture if you attempt to straighten it.     Been there done that. Plenty of variations and pattern parts so take extra care .

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Is your commando a Mk3 (disc) or a drum braked one? I have two spare g/boxes both handed for the Mk3, 1.25 to 1 ratio, one marked  BG5333/171 and another BG5330/164 

They don't need the spacer (06 7629) in the Mk3 application

  

 

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So has a drum brake.  When I bought the bike it didn’t have a spacer.  

Thank you for your replies.

 


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